(a) Field of the Invention
The present invention relates to an improved process and system for controlling welding operations and more particularly to a system and a process which controls the quality of a weld in relation to the actual shape of a joint to be welded between two metal pieces of a workpiece to be welded by detecting the thermal radiation energy emanating from the joint in close proximity to a welding element.
(b) Description of Prior Art
In accordance with a general feature, the present invention provides an accurate control of some operating conditions of the electrode of an arc welding machine, such as the electrode current position or the travelling speed of same by adapting such operating conditions to the particular configuration or geometry of the workpiece joint to be welded so as to form thereover an homogeneous and regular weld seam of a required quality. Such an adequate quality seam is of course obtained whenever the joint is properly tracked by the arc electrode and filled by the weld material during the welding operation, which implies more than just a center-line following or tracking of the workpiece joint. Heretofore, several mechanical devices have been attached to the electrode holder to track and position the electrode along a joint. However, these types of devices, although dependable where the joint presents a linearly extending constant width configuration, are still wholly ineffective when the workpiece joint is of irregular width or follows a rather awkward path, thereby producing a weld seam of poor or inacceptable quality.
With the advance of technology, more sophisticated systems were proposed to control the quality of the weld seam with most of those systems advocating the use of infrared radiation sensitive devices that collect the infrared rays emitted from a workpiece heated to a high temperature by a flame or an electric power arc, in the vicinity of the welding zone. For example, U.S. Pat. No. 2,089,015 discloses a system wherein a photo-electric cell is focused on the highly heated or fused metal adjacent or at the welding point in order to detect instantly changes in the welding zone above or below a predetermined normal condition so as to control the operation of the welding machine to ensure the welding of the gap between the plate edges by the welding material. However, the latter system does not provide any quality insurance as to the correctness and accuteness of the weld seam resulting from the welding operation.
U.S. Pat. No. 3,370,151 does provide a system effective in determining the correctness and regularity in width of the weld seam by detecting the sharp changes in temperature occurring at both edges of the seam by transverse scanning the seam with a photocell head. Such a system, however, has drawbacks in that where defects are detected, the welding operation has to be resumed again. Both above-mentioned prior art systems are totally ineffective in controlling accurately, by any means, the quality of a weld whenever a major irregularity occurs along the profile of a workpiece joint to be welded and further when the temperature dissipation in the vicinity of the welding zone is altered or impaired by the presence of elements such as heat sinks, grooves, or bores which considerably affect the dissipation rate of the heat generated by the arc electrode through the workpiece.